The present invention relates to a rear wheel suspension system of a motorcycle.
Generally, there has been adopted a swing-arm system for suspending a rear wheel of a motorcycle, and in such swing-arm system, a lateral pair of arm members arranged in parallel to each other are coupled at one ends at which the arm members are pivoted to a motorcycle body. Further, an axle of the rear wheel is supported by free ends of the arm members.
Furthermore, in a shaft-drive system of the type in which rotation of an engine of the motorcycle is transmitted to the rearwheel through a propeller shaft, a power transmission (unit) including, for example, a propeller shaft is housed in one of the arm members. This arm member is formed to be dividable along the axial direction of the propeller shaft, i.e. longitudinal direction of the motorcycle body.
In such conventional arrangement mentioned above, it becomes difficult to assemble and maintain the power transmission unit. More particularly, in a case where parts or members are disposed in a deep portion of the arm member or exchanged at such deep portion, it is required for a worker to disassemble or once remove all other parts including such as power transmission unit, which results in a bad operating property of the motorcycle.
An object of the present invention is therefore to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a rear wheel suspension system of a motorcycle providing an improved assembling performance and/or operating property.
This and other objects can be achieved according to the present invention by providing a rear wheel suspension system of a motorcycle in which an engine unit is mounted to a motorcycle body and a power transmission unit coupled to the engine unit is arranged to the motorcycle body to be swingable through a pivot shaft, the rear wheel suspension system comprising the power transmission unit, a pair of arm members disposed to lateral side portions of the motorcycle body in parallel to each other, and connection members connecting both end portions of the arm members, wherein one of the arm members constitutes the power transmission unit which has an inner hollow portion in which a power transmission member is accommodated and has a structure dividable into lateral two parts forming an arm base section and a cover section.
In a preferred example of the above aspect, the power transmission member is a propeller shaft, a bearing is formed in the cover section of the power transmission unit so as to support one end portion of the propeller shaft. One of the connection members connecting one endportions of the arm members constitutes a support member supporting the pivot shaft and wherein a swing motion center of a universal joint coupling the propeller shaft and a power output shaft of the engine unit is disposed on an extension of an axis of the pivot shaft.
At least other one of the arm members, the arm base section and connection members are formed through a casting process.
According to the present invention, swing-arm-type rear wheel suspension system includes the transmission unit composed of the arm base section and the arm cover section, so that the power transmission member disposed inside the transmission unit can be easily assembled and thus easily maintained and inspected.
Since the propeller shaft and the cover section is formed integrally to be detachable, the assembling performance and or operating property can be improved. The arrangement of the swing motion center of the universal joint on the extension of the pivot shaft axis makes it possible to smoothly transmit the driving force (speed) of the engine. The casting process can improve the rigidity and moldability of parts such as arm member, base section and connection member.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.